During the practice of an electric arc welding process, it is necessary, at the beginning of the welding operation, to establish an electric arc between a cathode and an anode.
In general, establishing the electric arc, also called striking, can be carried out in two ways, namely by a short circuit or by use of high voltage.
More precisely, striking of the short circuit type consists in placing the cathode and the anode in contact with each other.
In this manner, there is created, upon establishing the short circuit, a current flow which heats two ends of the electrodes facing each other and there is then produced an electric arc upon progressive separation of the two electrodes from each other.
This type of short circuit striking is used particularly for TIG (Tungsten Inert Gas) welding in which the cathode is constituted by a tungsten electrode and the anode is constituted by the piece to be welded.
Similarly, short circuit striking is also used for MIG (Metal Inert Gas) welding in which the anode is a fusible wire and the cathode, again, is the piece to be welded.
It is to be noted however that when the anode is a fusible wire, it is not necessary to move the end of the fusible wire away from the cathode, upon striking the arc, because the intensity of the current is generally sufficiently great to melt the end of said wire and thereby permit the arc to be struck.
It is also possible to use striking by short circuit when practicing plasma cutting or in a process of surface treatment with an electric arc.
However, striking by short circuit has a major disadvantage, namely, requiring contact between the cathode and the anode, said contact being apt to give rise to pollution or premature wear or the cathode, in particular, when the latter is a tungsten electrode, thus requiring its more frequent replacement.
Accordingly, in TIG welding, striking by short circuit gives rise to a frequent regrinding of the tungsten electrode.
Moreover, it has been noted that inclusions of tungsten were likely to be found in the weld bead, which is prejudicial and decreases the quality of said weld bead.
These problems can at least in part be solved by striking of the high voltage type.
Thus, this type of striking uses high voltage pulses and does not require direct contact between the anode, which is to say the piece to be TIG welded, and the cathode.
However, for reasons of cost and safety, the generation of high voltage generally implies that each of the high voltage pulses in fact be a high voltage damped oscillation.
The high voltage thus used effects a breakdown of the dielectric usually formed by the protective gas used, by rendering said dielectric electrically conductive and thereby permitting the passage of the current and the striking of an electric arc.
The greater the distance between the cathode and the anode, the greater the amplitude of the high voltage necessary to establish the electric arc.
The high voltage striking process is particularly used in TIG welding, in plasma cutting and in plasma welding. In this latter case, the arc is struck, first between two electrodes, then transferred to the piece to be welded by the plasmagenic gas flow.
Sometimes high voltage striking is also used in MIG welding, in particular in MIG welding in which during each half-cycle the voltage is zero and the wire not being in contact with the material to be welded, it may be necessary to restrike the electric arc.
However, high voltage striking also has itself a certain number of drawbacks.
Thus, the use of high voltages generally gives rise to substantial electromagnetic noise adapted to disturb considerably the electromagnetic environment of the welder and whose level is subject to strict regulation.
Thus, the level of disturbance is proportional to the electric power used during the striking phase of the electric arc and, no matter what the welding process which uses this high voltage striking, it is ordinarily necessary to minimize the amplitude of the high voltage necessary to establish said electric arc.
To minimize said amplitude of high voltage necessary to establish the arc, one can in certain cases use a cathode or an anode with a pointed end and/or a small anode/cathode distance.
This is for example the case when welding and plasma cutting in which the arc is struck in general between the nozzle and the electrode of the plasma welding torch used.
In manual TIG welding, the operator is himself obliged to position correctly and precisely the electrode relative to the piece to be welded, which is not easily carried out in practice, particularly when a welding mask is used.
Conversely, in the case of poor positioning of the electrode relative to the piece to be welded, the amplitude of the high voltage applied may not be sufficient to strike effectively an electric arc and/or an excessively long striking time may be needed.
It follows that it is accordingly necessary to increase the amplitude of the high voltage pulses, which permits increasing the tolerance as to the workpiece/electrode distance and/or the sharpening of the electrode, and can lead on the contrary to an unacceptable level of electromagnetic noise.